Transformer



July 22, 1952 E. .1. MACKERETH 2,604,519

TRNSFORMER Filed March 25. 1949 gu y ` overload capacity.

Patented July 22, 1952 UNITED .STATI-:s PATENT OFFICE t -TRANSFORMER tEdward J. Mackereth, Toronto, Ontario, Canada 'l Application March 2s,1949, serial No. 83,009

' part of my copending application, Serial Number 22,400, filed April2l, 1948, now abandoned.

An object of the invention is to provide a transformer of simple anddurable construction, which is not easily damaged in handling and whichis reliable in operation.

Another object is to provide a transformer of small overall size for itsnormal. and also for its Another object is to reduce the temperaturedifferential between different parts of the transtank.

Another object is to provide a transformer 8, Claims. (Cl. F75-361)which withstands high surges of voltage and current.

Afurther object of the invention is to provide a transformer in whichthe several turns of the primary winding are loaded substantiallysimultaneously due to the capacity effect` thereof and in which thepotential between the turns of the winding is reduced.

Another object of the invention is to provide a transformer in which theprimarywinding has a graded or varying capacitance tor ground to` reducesteep wave front surgesentering the primary winding and thus avoidsdanger to the winding due to such surges.

Another object of the invention is to provide transformer in which allof the windings have substantially the same surgeimpedance to avoidsetting up of dangerous oscillations in the windings, due to linetransients.

Other objects and advantages will hereinafter appear. l

The accompanying drawing is'illustrative of an embodiment of theinvention. In thedrawing,

Fig. 1 is a sectional view of a transformer em`- bodying the invention.

Fig. 2 is a sectional view on a plane at right angles to the sectionshown in Fig. l.

Fig. 3 is a vertical section of a fragment of windings embodying thepresent invention.

Fig. 4 is a fragmentary section 7of another embodiment of transformerwinding including the present invention; and

Fig. 5 is an enlarged fragment of Fig.. 4 to show the progressivevariation inl insulation as the cross sectional size of the conductorprogressively varies. e

Referring to the drawing, the transformer has a Arectangular laminatediron core Il] with Atwo vertical legs Il, |l,'joined at'vtheir. endby'cross members I2, l2, completing the closed iron magnetic circuit.The laminations of the core are clamped together byl suitable bolts-inany conventional manner. Attached `to each lower corner of the core isan angle bracket'l3 fastened by a bolt I4 to the bottom of an enclosingtank I5. rr

Each core leg Il is provided with a primary winding IB and asecondary'winding I1 concentric with the primary winding. .Both windingsare suitably insulated from the corey and from each other and suitablemeans (not shown) may be provided to support the windings rigidly lonthe core. The inner end (not shown) of the primary winding I6 may beconnected to the transformer core and thus to the tank lin-while thelatter in turn may be connected lto ground by a wire attached to a lugI8 on the tank. -The outer end of the primary winding is connected to alead-in Wire I9, which passes through an insulatingbushing 20, andterminates at a lterminal 2|, mounted on the upper end of the bushing.

By reference to Fig. 3, it will be seen that the primary lead-in Wire I9is larger than any of the turns of the primary winding i6 and that suchprimary winding is composed'of conductors of two different sizes, theturns 16a being materially larger than the turns Hic. For examplalayer|6a may be as largeas No. 6 B. & S. gauge while winding layers i may beas small as number 24 conductor on the same gauge. Only one layer ofturns Isa and several layers of turns, Hic are shown, but it will beunderstood that the; two or more layers of the heavier turns may be.used with a corresponding reduction in the number of turns of conductorIBC. The heavier turns Ita of the primary winding I6 have heavierinsulation than the rest of the winding to absorb the extra potentialstrain thereon due to voltage surges on the transmission line. When inaddition to the foregoing strengthening lof the insulation of the endturns, their cross section is also increased, the tendencykof shortcircuiting vdue to voltage surges on the line is greatly reduced. Thismay be due to the fact that a surge current which is impressed ontheseturns, due to a steep wave front, flows largely on the surface of thewire, resulting in high.v momentary current density which causes meltingof the surface metal and short circuits betweenturns andburnouts.Furthermore, and in addition yto greater momentary current-carryingcapacity, va 'larger cross section of the wires reduces the maximumpotential gradient between adjacent wires and this in itself reduces thestrain on their insulation and thus the tendency to cause shortcircuits.

The maximum graded capacitance effect would be obtained if it werepractically possible to make a conductor of a constantly decreasing sizeand to use such conductor for the primary winding, the smallest size ofthe conductor being equal to the size of the 'conductor in the secondarywinding. A close approximation of the maximum effeet can be obtained ifthe primary windingis made with turns Ia, turns IEb and turns IBc ofprogressively smaller size and down to the size of the conductor ofsecondary winding Il. It will be understood that any number of sizes ofconductors may be used in the-primary winding so long as the rst turnsare substantially thev size of the lead-in wire I9 and the last turnsare substantially the size o'f the conductor of the secondary winding. y

It has been found that even the construction of Fig. 3 will resistbreakdown at surges of up to 50,000 amperes per micro second and thestructure of Fig. i will withstand surges of even higher values. Hence,it is possible to obtain a transformer winding resistant to all of theaverage lightening surges and at a reasonable cost. The best result isobtained by the use of a large conductor at the line-connected end ofthe primary winding, by providing sufficient capacitance to reduce thesteep-wave fronts and by varying the capacitance to ground. Thepotential between larger size turns is reduced and all of the windingshave substantially the same surge impedance.

The secondary winding is arranged in two sections or coils l1, one oneach leg of the frame as is common practice. The two coils may beconnected in series or parallel. In the present case the two coils areusually connected in series to afford a 3-wire current supply. Thecommon center tap of the two coils is grounded to the tank l5, while theouter taps are connected by wires 22 and 23, respectively, to theterminal bushings 24 and 25, on top of the tank l5.

The tank l5 consists of two similar relatively shallow cups 26 and 21drawn or spun from sheet steel and provided at their edge with a shorttransverse flange 28. The bottoms 29 of the cups are relatively flat andmerge into the cylindrical sides in a curve of relatively large radius.

In assembling the apparatus the transformer core and windings areassembled in the usual manner. Thereafter the assembled transformer isfastened inside of the lower cup in the manner described. The bushings20, 24 and 25 are attached in any suitable manner to the top cup 2 ofthe tank l5. Thereafter the top cup 2 is put in position, while the leadwires I9, 22 and 23 are simultaneously threaded through their respectiveinsulating bushings and sealed therein in an air and moisture tightmanner. The ground wires are then connected to thevinside of the lowercup 26. The bottom and top cups 26 and 2l of the casing are now weldedtogether along the flanges 28, The welded flange forms a perimetricalbead, which serves as the support of the assembled transformer as willbe pointed out hereinafter. Thereafter the tank is filled with asuitable insulating liquid and may then be heated or treated otherwiseso as to drive out air and moisture entrapped in the liquid or in thetransformer coils.

The finished transformer may be mounted on a transmission pole or othersupporting structure by means of a bracket assembly arranged to embracethe tank and permit its rotation to bring the terminals of thetransformer into the most advantageous position relative to the linewires to which they are connected. The assembly comprises a length ofvertically extending channel iron or the like 4D provided with suitableholes for fastening to a supporting pole or wall. A circular iron ring4| of strap iron and of a diameter about equal to the outer diameter ofthe tank l5, has its two adjacent ends welded together and bridged by aU-shaped strap 42 of rectangular section whose intermediate and endportions are welded to the ring 4I and also to the channel 40, thusjoining the former and the latter to form a rigid support.

Various other modifications within the scope of the present inventionwill be apparent to those skilled in the art.

What I claim as new and desire to secure by Letters Patent is:

l. In an electrical transformer, an electrically conductive case, alead-in conductor extending into the case in insulated relationtherewith, a primary winding connected at one end with the case and atthe other end with 4the lead-in, the primary winding being formed ofportions of conductor of progressively decreasing cross-section from awinding end connected with the leadin to a winding end connected withthe case, the conductor of the portion connected with the leadin beingof larger size than the conductor of the portion connected with the casefor varying the capacitance of the winding from a large value in theportion connected with the lead-in to a lesser value in the portionconnected with the case, a secondary winding comprising a conductorinductively related to the primary winding, and terminals extending fromthe secondary winding exteriorly of the case and in insulated relationtherewith.

2. In an electrical transformer, an electrically conductive case, alead-in conductor extending into the case in insulated relationtherewith, a primary winding connected at one end with the case and atthe other end with the lead-in, the primary winding being formed ofportions of conductor of progressively decreasing cross-section from awinding end connected with the lead-in to the winding end connected withthe case, a secondary winding conductor inductively related to theprimary winding, and terminals extending from the secondary windingexteriorly of the case and in insulated relation therewith, the portionof the primary winding conductor connected with the lead-in being ofsubstantially the size of the lead-in and the portion of the primarywinding conductor connected with the case being substantially the sizeof the secondary winding conductor for varying the capacitance of theprimary winding in its length from :t large value at the lead-inconnection to a lesser value at the connection thereof with the case.

3. In an electrical transformer, an electrically conductive case, alead-in conductor extending into the case in insulated relationtherewith, a primary winding connected at one end with the case and atthe other end with the lead-in, the primary winding being formed ofportions of conductor of progressively decreasing cross-section from awinding end connected with the lead-n to the winding end connected withthe case, a secondary winding conductor inductively related to theprimary winding, and terminals extending from the secondary windingexteriorly of the case and in insulated relation therewith, the primarywinding conductor comprising a portion connected with the lead-in and ofsubstantially the size thereof, a portion connected with the case and ofsubstantially the size of the secondary winding conductor and a portionintermediate said primary winding portions and of a size between thesizes of the nrst said two of the primary conductor portions whereby thecapacitance of the primary winding is reduced in its length from thelead-in connection to the connection thereof with the case.

4. In an electrical transformer, an electrically conductive case, alead-in conductor extending into the case in insulated relationtherewith, a primary winding connected at one end with the case and atthe other end with the lead-in, the primary winding being formed ofportions of conductor of progressively decreasing cross-section from awinding end connected with the lead-in to the winding end connected withthe case, a secondary winding conductor inductively related to theprimary winding and of the same crosssectional size throughout itslength, terminals extending from lthe secondary winding outside of thecase and in insulated relation therewith, and insulation on the primaryand secondary windings, the primary Winding insulation progressivelydecreasing in insulating value as the conductor size decreases, theprimary winding conductor comprising a portion connected with thelead-in and of substantially the size thereof, a portion connected withthe case and of substantially the size of the secondary windingconductor and a portion intermediate said primary winding portions andof a size between the sizes oi the rst said two of the primary conductorportions whereby the capacitance of the primary winding progressivelydecreases along its length from the lead-in connection to the connectionthereof with the case.

5. In an electrical transformer, an electrically conductive case, alead-in conductor extending into the case in insulated relationtherewith, a primary winding conductor connected at one end with thecase and at the other end with the leadin, the primary winding beingsubstantially of hollow cylindrical shape and being formed of portionsof conductor of progressively decreasing cross-section and wound inlayers and connected at the ends respectively with the case and with thelead-in conductor, the layer of primary winding conductor connectedV atone end with the lead-in being of larger cross-sectional size than thelayer of conductor connected at one end with the case for varying thecapacitance of the primary winding from a larger value in the portionconnected with the lead-in toV a smaller value in the portion connectedwith the case, a secondary winding conductor inductively related to theprimary winding, and terminals extending from the secondary windingexteriorly of the case and in insulated relation therewith.

6. In an electrical transformer, an electrically conductive case, alead-in conductor extending into the case in insulated relationtherewith, a primary winding comprising a conductor with portions ofprogressively decreasing cross-section from a, winding end connectedwith the lead-in to a winding end connected with the case and beingwound in layers of substantially hollow cylindrical shape, secondarywinding conductor inductively related to the primary winding, andterminals extending from the secondary winding outside of the case andin insulated relation therewith, the outer peripheral layer of theprimary winding conductor being connected at one end with and being ofsubstantially the size of the lead-in and the inner peripheral layer ofthe primary winding conductor being connected at one end with the caseand being substantially of the size of the secondary winding conductorfor reducing the capacitance of the primary winding from a large valuefor the outer peripheral layer to a smaller value for the innerperipheral layer of the primary winding.

7. In an electrical transformer, an electrically conductive case, alead-in conductor extending into ythe case in insulated relationtherewith, a primary winding comprising a conductor with portions ofprogressively decreasing cross-section from a winding end connected withthe lead-in to a winding end connected with the case, a secondarywinding conductor inductively related to the primary winding andterminals extending from the secondary winding outside of the case andin insulated relation therewith, the primary winding being ofsubstantially hollow cylindrical shape and comprising a layer connectedat one end with and of substantially the cross-sectional size of thelead-in conductor and c, layer connected at one end with the case and ofsubstantially the cross-sectional size of the secondary windingconductor for progressively decreasing the capacitance of the primarywinding from the end connected with the lead-in conductor to the endconnected with the case.

8. In an electrical transformer, an electrically conductive case, alead-in conductor extending into the case in insulated relationtherewith, a primary winding comprising a conductor with portions ofprogressively decreasing cross-section from a winding end connected withthe lead-in to a winding end connected with the case, a secondarywinding conductor inductively related to the primary winding, terminalsextending from the secondary winding outside of the case and ininsulated relation therewith, and insulation on the primary andsecondary winding conductors proportional in insulating value to thesize of the conductors, the primary winding being of substantiallyhollow cylindrical shape and comprising an outer peripheral layer ofconductor connected at one end with and of substantially thecross-sectional size of the lead-in conductor, an inner peripheral layerof conductor connected at one end with the case and of substantially thecross-sectional size of the secondary winding and an intermediate layerof conductor of a crosssectional size between the sizes of the conductorof the peripheral layers of the primary winding for progressivelydecreasing the capacitance of the primary winding in steps from thelead-in connection therewith to the case connection therewith.

EDWARD J. MACKERE-TH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date '714,934 Moody Dec. 2, 1902783,802 Shoemaker Feb. 28, 1905 854,774 Taylor May 28, 1907 1,872,369Van Sickle Aug. 16, 1932 1,940,840 Bellaschi Dec, 26, 1933 2,519,224Chiles, Jr Aug. 15, 1950

